What It Is	Nuisance dinoflagellate microorganisms
Looks Like	Brown snotty strings with bubbles
Main Cause	Ultra-low nutrients / sterile tank
Difficulty	Hard — the tricky one
Best Fixes	RAISE nutrients, biodiversity, UV

Overview

Dinoflagellates are the pest that breaks the usual rules. Most nuisances thrive on high nutrients; dinos often explode when nutrients are too low — a sterile, over-cleaned tank with nitrate or phosphate bottomed out at zero. They’re also genuinely hazardous: some strains are toxic and can wipe out a cleanup crew. Beating dinos usually means doing the opposite of what you’d do for algae: rebuild nutrients and biodiversity so other microorganisms out-compete them.

How to Identify It

Brown, tan, or mustard stringy snot that coats rock, sand and corals, typically studded with oxygen bubbles, growing through the day under light and often receding at night. It’s slimy and stringy rather than hairy, and it comes back within hours of removal. If your cleanup crew is mysteriously dying, suspect toxic dinos.

How to Get Rid of It

Raise nutrients into a normal range — get nitrate to roughly 5–10 ppm and phosphate around 0.03–0.1 ppm (feed more, dose if needed). This alone reverses many dino outbreaks by letting competitors return.
Boost biodiversity — add live rock/sand from a clean established tank, and bacterial/phyto products, so a healthy microfauna crowds dinos out.
UV sterilizer — very effective on the free-swimming stages; run one alongside the nutrient fix for a faster knockdown.
Manual + blackout support — siphon mats out, and a 3-day blackout with the skimmer wet can help — but only with the nutrient/biodiversity work, not instead of it.

Prevention

Don’t chase zero nutrients. The single best dino prevention is a mature tank with stable, non-zero nitrate and phosphate and good biodiversity. Avoid over-skimming, over-GFO, and aggressive “polishing” that sterilizes the system — that emptiness is exactly the vacuum dinos fill.

What Doesn’t Work

Treating dinos like algae and slashing nutrients: the classic mistake — it feeds them. Handling toxic strains carelessly: some release toxins; wash up and don’t let a big die-off crash the tank. One-and-done blackout: without raising nutrients and biodiversity, dinos return — this pest needs the ecosystem rebuilt, not just removed.